The present invention relates to wood or coal fueled heating systems and, in particular, to a self-contained furnace which mounts externally of the structure or premises being heated.
With increasing heating fuel costs for gas and petroleum products, alternatively fueled heating systems have experienced a resurgence in popularity. Wood and coal fired stoves, boilers and furnaces are increasingly being used as the primary or as a supplemental heat source. This is especially true in the northern-tier states where alternative, low-cost fuel supplies are available and winters tend to be long and cold.
Many of these stoves mount within the structure being heated. That is, the heating appliance is typically contained within a utility room or finished room of the dwelling. Either radiant heat is obtained or an intermediate heat exchange carrier or media is heated and conducted about the premises.
Unfortunately, the increased use of fuels that produce relatively large amounts of creosote and improper stove and flue maintenance has resulted in increased numbers of related fires and resultant increased insurance premiums. Many manufacturers of stoves and furnaces intended for use as primary heating systems, therefore, now construct there stoves as self-contained assemblies. These assemblies are mounted external to the premises to be heated. The risk of fire and smoke damage to the premises is thereby reduced.
With the removal of the firebox from the premises, larger fireboxes become more practical, along with longer burn times between each recharging or refueling. Consequently and depending upon the fuel, burn times of one to multiple days can be obtained between each re-charging of the stove. Stoves may now also be used over a longer heating season, since the residual radiant heat does not overheat the premises during milder fall or spring days. As these stoves are also made to burn more efficiently, the flue temperatures have been reduced.
With reduced flue temperatures, however, increased amounts of creosote and water vapor are created which can significantly reduce the life of the firebox, especially where a top mount flue is provided. That is, large amounts of moisture accumulate as part of the combustion process and can amount from one to many quarts a day. This water accumulates in the ash to form an acidic lye compound which corrodes away the firebox in a matter of months.
An additional problem effecting the cost of the stove and operational safety can develop at the fire door. Depending upon the stove construction, warpage can occur in the door during the normal cycling of the stove. The warpage may be significant or not and may even permanently effect the door. In all cases, however, warpage tends to create unintended drafts and unregulated burning. A non-warping door construction is therefore desired.
With the foregoing considerations in mind, applicant has developed an improved self-contained wood or coal fueled furnace.